Introduction
Don't you find you have written the same segment of code many times to parse a subtree because the action you wanted to launch on the items was different. In order to avoid such code, I've written CTreeViewIterator
class. This class contains a method called ApplyFunction
to launch a function on each item/node of a subtree.
Implementation
The class I've written is dedicated to Explorer like applications (those with a CTreeView
class on the left side). In that section, we're going to see how to use CTreeViewIterator
in that general case. In the section Adaptation, we'll see how to modify it to use it in other cases.
When you generate your application using the wizard, Visual C++ doesn't give you the capability to choose the CTreeView
class implementation. Therefore, you have to have a CLeftView
in your application. In the LeftView.cpp file, add the following line in the include
section.
#include "TreeViewIterator.h"
You're now able to use the CTreeViewIterator
class in that module.
You must define the function that will receive the item/node as parameter. This function will be external to your CLeftView
class even if defined in the same module. If you don't define it in this module, do not forget to create a definition to set it visible from this module. If for any reason, you do want to set it as a method of your CLeftView
class, please read the Adaptation section. The signature of this function is predefined. It must be like this:
int ExternalFunction ( CLeftView *tvTreeView,
HTREEITEM tiItem )
- This function must return an integer set to
1
if ok, 0
else. - The first parameter is to be a
CLeftView*
. It will receive a handle on the CLeftView
to let you use. - The second parameter is to be a
HTREEITEM
. It will receive a handle on the currently parsed item/node.
For example, let's consider this function:
int ExternalDisplayItem (
CLeftView *tvTree,
HTREEITEM tiItem )
{
CTreeCtrl &tTree= tvTree->GetTreeCtrl ();
tvTree->sFullList += tTree.GetItemText(tiItem) + "\r\n";
return ( 1);
}
The goal here, is to store the subtree as a list in a string
. So, the only thing the external function has to do is getting the name and concatenating it to the full list. To do so, it will use an attribute created in the CLeftView
called sFullList
(type CString
). Since we got a handle on the CLeftView
as first parameter, there's no problem till the attribute is public
(if not, we should have used public
methods like get
& set
). Using this method, you may update the tree item/node or the CLeftView
the way you want.
Now you have the function to apply to each item/node, you have to call it. To do so, you'll have to implement first the iterator and then, to call the ApplyFunction
method with the right parameters.
The ApplyFunction
's signature is:
int CTreeViewIterator::ApplyFunction (
CLeftView *tvView,
HTREEITEM tiStart,
FuncPtrView fptrFunction )
- This function returns an integer set to
1
if ok, -1
if problem when parsing subtree, 0
if problem when calling the external function. - The first parameter is a handle on the
CLeftView
derived from CTreeView
. - The second parameter is a handle on the item/node to consider as the root when parsing the subtree.
fptrFunction
is a function pointer to the external function you previously created.
Using our precedent external function, we got this code:
void CLeftView::OnSelchanged (
NMHDR *pNMHDR,
LRESULT *pResult )
{
NM_TREEVIEW *pNMTreeView = (NM_TREEVIEW *) pNMHDR;
CTreeCtrl &tTree = this->GetTreeCtrl ();
CTreeViewIterator *ptrTree = (CTreeViewIterator *) &tTree;
sFullList= "";
ptrTree->ApplyFunction (this, pNMTreeView->itemNew.hItem,
&ExternalDisplayItem );
GetDocument()->UpdateAllViews ( this, 1L, (CObject *) &sFullList );
*pResult = 0;
}
The method OnSelChanged
is launched when the user has selected a new item/node in the treeview
. Here, we have caught it to add our function call. As you can see, we first add the iterator implementation with:
CTreeViewIterator *ptrTree = (CTreeViewIterator *) tTree;
In fact, we may consider the iterator on the CTreeCtrl
as a shell with a special method. Therefore, within ApplyFunction
method, we will see the content of the CTreeCtrl
to parse.
We now have to get the parameters:
That way, we obtain the following call:
ptrTree->ApplyFunction (this, pNMTreeView->itemNew.hItem, &ExternalDisplayItem );
Since this event may be caught many times, we initialize the variable sFullList
before we parse the subtree.
When the ApplyFunction
is finished, we update the other views with the generated string
using the method UpdateAllViews.
Here we are, catching the UpdateAllViews
event isn't the subject here but you may have a look at the sample project to get an idea.
Adaptation
That section is to explain you how to upgrade the CTreeViewIterator
to adapt it to your own case. I wrote it as a FAQ. I'll update it with the cases you will propose. So, what's your problem?
Question: My CTreeView
class is not named CLeftView
.
Answer: Change the CTreeView
classname in:
- The function pointer's signature
- The
ApplyFunction
definition - The
ApplyFunction
implementation
Question: I want to set the called function a method of my class CLeftView
.
Answer: You just have to change the function pointer's signature to add your class. For example, try this:
- Change the External function to a
public
method called DisplayItem
in CLeftView
class. - Change the signature to:
typedef int ( CLeftView::*FuncPtrView ) ( CLeftView * tTree, HTREEITEM tiItem );
- Change the call of
ApplyFunction
method to:
ptrTree->ApplyFunction (this, pNMTreeView->itemNew.hItem, &CLeftView::DisplayItem );
- In
ApplyFunction
implementation, change the function call to:
( tvView->*fptrFunction ) ( tvView, tiCurrItem )
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